Screening of critical parameters influencing thermal-hydraulic reliability of simple passive system

Robust safety nature of passive safety systems (PSSs) accounts for their increasing applications. Critical parameters (CPs) which influence reliability of thermal-hydraulic (t-h) PSSs are considered independent in most cases while considering their effects purposely for simplicity which may not be realistic. Findings affirmed reliability of t-h PSSs to be influenced by CPs that are dependent in most scenarios and thus, effects of CPs dependency which can directly/indirectly influence t-h reliability need to be considered. Reliability assessment methodologies (RAM) can thus be improved upon by considering the dependency of CPs in reliability analysis. In this regard, this paper considers the screening of CPs required to justify their dependency consideration in evaluating t-h reliability. The Pearson's product moment correlation coefficient and covariance method were applied as illustration for the screening of the possible realistic CPs, which affect natural circulation of a passively water-cooled steam generator. The approach was used to determine the combinations of the CPs that are dependent and screens out those adjudged independent. Based on the results obtained, appropriate considerations (dependency/independency) can be made and further analysis of interest (failure/reliability) can be conducted for the system. Incorporation of this screening approach into the existing t-h RAMs will improve their efficiency. (author)